Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $115.81   8.751%   $125.9445   $125.94   $125.95   $125.90  
  Purchase #2 $227.29   10.249%   $250.585   $250.59   $250.60   $250.60  
  Purchase #3 $11.46   8.372%   $12.4194   $12.42   $12.40   $12.40  
  Purchase #4 $117.31   6.575%   $125.0231   $125.02   $125.00   $125.00  
  Purchase #5 $28.77   9.384%   $31.4698   $31.47   $31.45   $31.50  
  Purchase #6 $59.37   3.475%   $61.4331   $61.43   $61.45   $61.40  
  Purchase #7 $138.67   5.833%   $146.7586   $146.76   $146.75   $146.80  
  7 purchase totals = $698.68       $753.6335   $753.63   $753.60   $753.60